Mining roof support cylinder corrosion protection apparatus and method

ABSTRACT

A roof support for an underground mine which has a hydraulic cylinder positioned between a roof engaging support and a ground engaging base and has a flexible gas barrier or enclosure surrounding surfaces of said hydraulic cylinder which are subject to corrosion by gases present in the underground mine. Continuous flowing non-corrosive gas such as nitrogen is supplied to a space between the gas barrier and said hydraulic cylinder for preventing corrosion of cylinder surfaces by corrosive gases present in the mine which may include hydrogen sulfide.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a corrosion protection system and a method ofprotecting certain articles from corrosion by enclosing the articles ina suitable enclosure and flushing the interior space of the enclosurewith a continuous flow of non-corrosive gas, thereby preventing ambientcorrosive gasses (or other corrosive agents) from contacting theprotected articles.

This invention relates to movable, semi-permanent or temporary roofsupports and cylinders used in coal mining or other underground mining.Movable, semi-permanent or temporary roof support apparatuses generallyemploy a roof engaging support and a ground-engaging base with hydraulicroof support cylinders positioned between a roof engaging support and aground-engaging base. Hydraulic roof support cylinders are used in coalmining operations where gases or other agents, which are corrosive tocylinder exterior surfaces, may be present.

2. Description of Related Art

Temporary roof supports including temporary roof support cylinders asdescribed in U.S. Pat. Nos. 5,950,673 and 5,026,218 are manufactured andsold by Joy MM Delaware Inc. The Joy roof support structure depends upona hydraulic roof support cylinder which is plated with bronze and whichis wiped infrequently by hydraulic fluids during use. As manufactured byJoy Mining Machinery, the roof support cylinders are coated with bronzefor corrosion protection purposes. The cylinders may also be coated withother substitutions for bronze and brass. However, bronze was found intesting to be the best with Hydrogen sulfide. However, this material iscorroded by at least hydrogen sulfide and, therefore, the cylindersrequire protection from prolonged contact with hydrogen sulfide gasses.During use, a roof support may be put in place with cylinders in anextended position, or only partially collapsed, thereby leaving at leastsome of its surfaces exposed for an extended period of time. This isespecially true of semi-permanent roof supports as used in miningoperations known as “longwall”. When bronze or other copper containingsurfaces are exposed to atmospheres which may include hydrogen sulfidewith possible high humidity conditions, corrosion of the bronze or otherplating becomes severe. When cylinders are severely corroded, thecylinder is no longer capable of operation because of leakage athydraulic cylinder seals. Under certain mining conditions, as many as 35percent of the cylinders used in a mine may require replacement withinone year, resulting in possible replacement of 130 cylinders per year inone mining operation. The replacement or repair of each cylinder costsin the order of $40,000 for a cost of $5,000,000 per year.

In the art of mining where coal gob is present, nitrogen gas may also besupplied to the mine in order to decrease the danger of mine fires, orto provide rapid introduction of nitrogen in the case of emergency.“Gob” is collapsed roof strata, often containing coal that is leftbehind in a mine behind a longwall as it advances. Therefore, nitrogen,which is a known non-combustible and non-corrosive gas, is readilyavailable in certain mining operations. Nitrogen is used to dilutemethane and oxygen gases in a mine and is readily available as a gaswhich can be used to protect against corrosion. However, it is to beunderstood that any inert gas or gas which does not attack a hydrauliccylinder may be used such as clean air.

U.S. Pat. No. 6,551,552 to Lyublinski relates to corrosion protectionand protecting an article from corrosion by placing an article in a gasimpermeable enclosure. This prior art differs from Applicant's inventionin that Applicant maintains open orifices and a small positive pressurewithin the gas enclosure which continually flushes the gas enclosurewith the inserted non-corrosive gas (nitrogen). The '552 patent furtherfails to suggest or teach any possible utility for protection of bronzeplated cylinders which are subject to corrosion by hydrogen sulfide gasin coal mines. '552 recognizes the corrosive nature of sulfides, and thesusceptibility of copper, bronze and brass to certain corrosion undernormal atmospheric conditions. As taught by '552 in column 3, the gasimpermeable enclosure would have no tears, leaks or pinholes which wouldallow the higher internal pressure to equalize with the slightly lowerexternal pressure. Applicant's invention, on the other hand, providesfor continuous controlled flow and an orifice to the outside to controlpressure on the inside.

BRIEF SUMMARY OF THE INVENTION

Observing the high cost associated with the need for replacement roofsupport cylinders in a mine where hydrogen sulfide or other corrosivegas is present, Applicant has conceived of the idea of use of thenitrogen gas available in the mine to shield bronze coated roof supportcylinders from attack by hydrogen sulfide gas. Other cylinder metals andnon-corrosive gases may also be used. The nitrogen, or othernon-corrosive, gas is fed to a flexible plastic gas barrier whichsurrounds the roof support cylinder and which flows through the areasurrounding the roof support cylinder. The nitrogen gas purges corrosivegas from the area of the roof support cylinders and leaves the roofsupport cylinder exposed only to the non-corrosive or nitrogen gasses.The gas barrier surrounding the roof support cylinders has a gas exitorifice, which maintains a slight positive pressure within the roofsupport cylinders enclosure.

For roof support cylinders, it is estimated that a complete replacementcost would be $40,000 per cylinder while repair costs would be in theorder of $20,000 per cylinder. On the other hand, it is estimated thatcosts of approximately $1,000 per cylinder will be required to utilizethe method and apparatus of this invention. This provides a substantialcost saving and it has not been recognized by those in the industry. Theenclosure may be a rubber bellows bag or the like fastened and sealed tothe cylinder at the top and bottom by hose clamps or any other clampingmeans.

The method of this invention applies to mining equipment used in certainunderground coal mines. Currently exposed metal surfaces are subject toa corrosive environment by hydrogen sulfide gas and water spray mist.Corrosion has been especially severe on surfaces containing copper basedalloys, such as bronze. Due to the corrosion, the life of certain partsof costly mining equipment is shortened significantly.

As a part of the mining process, nitrogen is introduced to suppresspossible combustion of waste coal in mined out areas. This waste coaland roof strata, or gob, is present in areas that have been subjected tolongwall mining operations. Air or oxygen, in the gob, can causespontaneous combustion, therefore nitrogen is used to flush or diluteair and oxygen from the gob. The method of this invention can utilizethe existing nitrogen supply system (or other non-corrosive gas supply)to create a non-corrosive environment immediately adjacent to corrosionsensitive metal surfaces. By flushing an enclosure with a continuousflow of non-corrosive gas, a non-corrosive environment is created, theprotected metal surfaces and corrosive gases are prevented fromcontacting the surfaces, and the metal surfaces are protected.

The method of this invention prevents costly rebuilding and replacementof parts or the need for corrosion resistant alloys, and avoids the useof more costly corrosion protection methods using sacrificial barriers.The system is designed to be low cost and easily installed and removedfor maintenance.

This invention incorporates an enclosure sized to completely coverarticles to be protected. The enclosure(s) are provided with portsallowing gas introduction and gas exhaust from the interior of theenclosure. The enclosure need not be hermetically sealed or even tightlysealed, as the continuous flow of non-corrosive gas will flush awaycontaminating gases.

This invention comprises a roof support for an underground minecomprising in combination: a roof engaging support; a ground engagingbase; at least one hydraulic cylinder positioned between said roofengaging support and said ground engaging base; a flexible gas barriersurrounding surfaces of said hydraulic cylinder which would otherwise besubject to corrosion by gases present in said underground mine; andnon-corrosive gas supply for supplying a gas to a space between said gasbarrier and said hydraulic cylinder, and wherein said gas is nitrogen orother suitable gas. The apparatus also has a pressure release orificefor creating a positive pressure within said gas barrier with respect toambient pressure when non-corrosive gas is supplied to said space. Thismethod also comprises a method for protection of exposed metal surfacesin a coal mine or other mines comprising the steps of: placing metallicparts in a coal mine having a corrosive gas; creating a non-corrosiveenvironment immediately adjacent to corrosion sensitive metallic parts;placing said metallic parts in an enclosure; and introducing a flow of anon-corrosive gas into the enclosure; wherein said mine atmosphereincludes hydrogen sulfide or other corrosive agents and said exposedmetal surfaces contain a copper base alloy or other material subject tocorrosion and wherein the non-corrosive gas is nitrogen or othernon-corrosive gases. The enclosure can also be put on before items areplaced in the mine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a roof support cylinder and roof support which includes agas barrier enclosure in accordance with this invention.

FIG. 2A shows an upper flange in an open position which can clamp aroundthe top of a roof support cylinder.

FIG. 2B shows an upper flange in a closed position.

FIG. 2C shows a lower flange which can clamp around a bottom cylinder ofa roof support cylinder with a nitrogen supply and valves shownschematically.

FIG. 2D shows a lower flange in a closed position with a nitrogen supplyand valves shown schematically.

FIG. 3 shows a fully extended roof support with a gas enclosure andflanges shown in FIGS. 2B and 2D.

FIG. 4 shows a partially extended roof support cylinder with theenclosure partially collapsed.

FIG. 5 shows a completely collapsed roof support cylinder with theenclosure fully collapsed.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1 there is shown a typical mine roof support 10. The support hasa ground-engaging base 11 and a roof-engaging canopy or roof engagingsupport 12, a rear shield 13 and pivoting links 14. There are pair ofhydraulic support legs 15 which act between the roof engaging support 12and the base 11. The hydraulic cylinder roof support legs 15 may notnormally experience repeated full extension and retraction when the roofsupport 10 is in place during mining operations. This exposes thesurfaces of the hydraulic legs 15 to corrosive gases within the mine forlong periods where the hydraulic cylinder legs 15 are not wiped with ahydraulic fluid to form any barrier against corrosion. Therefore,corrosion is likely to occur and does occur on the surfaces of bronzeplated hydraulic cylinder legs or cylinders with other surfacematerials, especially in mines where hydrogen sulfide gas is present.

In FIG. 1, there is shown a nitrogen or other non-corrosive gas supply16, a control valve 17, and a pressure reducing valve 18 which supplieslow pressure nitrogen gas to an enclosure 19. Enclosure 19 is a flexiblegas barrier which is attached to a lower cylinder and upper cylinder ofa hydraulic cylinder by means of lower 32 and upper 30 flanges.

As shown in FIG. 3, the enclosure 19 comprises a flexible plastic,rubber, or otherwise suitable enclosure member 20 which is placed aroundthe hydraulic cylinder 21 of the hydraulic leg assembly 15. The legassembly is fixed to the base 11 and the flexible enclosure 20 isattached at the lower and upper portions as shown in FIGS. 1, 3, 4 and5. FIG. 4 shows the hydraulic leg partially collapsed, lowering theupper portion of the hydraulic cylinder 21, and FIG. 5 shows thehydraulic leg in a completely collapsed position with the plasticenclosure folded upon itself.

In FIGS. 2A and 2B there is shown an upper flange 30 which forms anupper portion of enclosure 19. The upper flange 30 engages an upperportion of the hydraulic cylinder 21 of hydraulic leg 15. The flange isclamped around the upper portion of cylinder 21 and provides a means forattaching a plastic enclosure 20 at its periphery. In the flange 30,there is provided one or more pressure release orifices 31. The pressurerelease orifice is sized so that there will be a continuous exhaust flowof non-corrosive gas (nitrogen) during the period when gas is suppliedto the enclosure 19. The size of orifice 31 is dependent upon thepressure and flow rate of the gas flowing into the enclosure which iscontrolled by valve 17.

FIGS. 2C and 2D show a lower flange 32 which clamps around a bottomportion of the hydraulic leg 15 or hydraulic cylinder 21. The lowerflange forms a bottom portion of enclosure 19. The lower flange is shownin an open position in FIG. 2C and in a closed position in FIG. 2D. Gasflows into the enclosure 19 through an opening 33 in the lower flange32. Still further, in accordance with this invention, the upper flangeand lower flange functions may be reversed, thereby placing a pressurerelease orifice on the lower flange and an inlet port or opening on theupper flange.

Non-corrosive gas is introduced into the enclosure at a pressure andflow rate that allows for suitable flushing against the variablepressure outside the enclosure. The flow rate is determined by the gasfeed pressure, the pressure limits of the enclosure and its fasteningsand the size and adjustment of the exhaust ports. The exhaust ports areshown as fixed orifices, however, they may have a variable or adjustablesize and, along with the flow control valve, can be used to adjust theflow, maintaining a nominally positive pressure inside the enclosurecompared to variable ambient conditions.

Nitrogen or other non-corrosive gas, which is otherwise available incertain coal mines having a methane gas concentration or spontaneouscombustion of gob problem, or which may be available for the purpose ofprotecting the cylinders only, is fed to the enclosure 19 through avalve 17 which is a control valve for turning on and off the nitrogensupply. Valve 18 is a pressure reduction valve which reduces pressure toa low level, such as two or three inches water column, in order toprovide a very slight positive pressure within the enclosure withrespect to the mine ambient pressure. This pressure in the enclosure iscontrolled by sizing orifices 31 in the upper flange, as well as valveson the inlet and/or adjustable valves at the outlets. For example, anR400 Regulator manufactured by Maxitrol can be used to provide an outletpressure of four inches water column at the lower flange. To provide a100 cubic foot per hour flow rate with an exhaust velocity of 10 feetper second, a total area of 0.4 square inches for the exhaust ports canbe used. Eight-quarter inch diameter holes will provide an appropriatesize.

The enclosure 19 may be made of a flexible plastic material with asealable longitudinal split which runs vertically along one side. Thisenables the enclosure, along with the upper flange 30 and the lowerflange 32, to be wrapped around the hydraulic cylinder 21 withoutremoval of the hydraulic cylinder 21 from the roof support assembly 10.This system and apparatus provides for protection against hydrogensulfide corrosion or other corrosive agents of cylinders of the typedisclosed herein without disassembly of the roof support 10. The upperand lower flanges 30 and 32 are clamped around the cylinder 15 and thelongitudinal split is closed to complete the enclosure.

Hose clamps may be used as collars around the top and bottom ofhydraulic roof support cylinders. The extensible enclosure is attachedto flanges 30, 32 on each end or directly to cylinders with hose clampsor other clamping means. One flange shield is used to introduce thenitrogen or other non-corrosive gas into the enclosure and the otherflange shield is used to support exhaust ports.

In a mine which uses nitrogen purge to reduce methane levels or oxygenlevels in gob, the nitrogen becomes essentially free because the amountof nitrogen which bleeds from pressure release orifices 31 is very smallwhen compared to that used to suppress spontaneous combustion.

This invention incorporates a plastic or other flexible enclosure sizedto completely cover any particular metal surface or other article, withseals similar to Velcro, taped or zip lock seals to allow placement andremoval of the enclosure and collared parts, allowing gas introductionand gas exhaust from the interior of the enclosure. For cylindricalobjects (hydraulic cylinders), flange shields are used as collars oneach end of the cylindrical object. The plastic or other suitableflexible enclosure is adhered to the flange shields on each end with alongitudinal seal on the plastic shielding enclosure and the flangesaligned. One flange shield is used to introduce nitrogen or othernon-corrosive gas into the enclosure and the other flange is used tosupport exhaust ports.

1. A method for protection of exposed metal surfaces in a coal minecomprising the steps of: placing parts in the coal mine having acorrosive gas; and creating a non-corrosive environment immediatelyadjacent to corrosion sensitive parts.
 2. The method in accordance withclaim 1 further comprising the step of creating a non-corrosiveenvironment comprises the steps of: placing said parts in an enclosure;and introducing a continuous flow of a non-corrosive gas into theenclosure.
 3. The method in accordance with claim 1 wherein saidcorrosive gas includes hydrogen sulfide and said parts have exposedmetal surfaces containing copper based alloy.
 4. The method inaccordance with claim 2 wherein the non-corrosive gas is nitrogen. 5.The method in accordance with claim 2 further comprising the step ofintroducing the non-corrosive gas at a positive pressure with respect toan ambient pressure in said coal mine.
 6. The method in accordance withclaim 2 further comprising a step of continuous flushing of saidenclosure with the non-corrosive gas.
 7. The method in accordance withclaim 2 further comprising enclosing said metallic parts in a plastic orother flexible container having seals along at least one side and atleast one opening at an end which allows a flow of non-corrosive gas toescape.
 8. The method in accordance with claim 2 further comprisingcontinuous flushing of corrosive gas away from said metallic parts. 9.The method in accordance with claim 7 further comprising sealing atleast one end with flange seals and attaching a nitrogen or othernon-corrosive gas source to said enclosure.
 10. The method in accordancewith claim 2 further comprising a fixed or an adjustable exhaust port tomaintain a positive pressure within said enclosure with respect toambient conditions.
 11. The method in accordance with claim 2 furthercomprising the step of maintaining a flow of the non-corrosive gas intoand out of the enclosure by controlling pressure of incomingnon-corrosive gas and sizing of an outlet opening fixed size oradjustable exhaust port.
 12. A roof support for an underground minecomprising in combination: a roof engaging support; a ground engagingbase; at least one hydraulic cylinder positioned between said roofengaging support and said ground engaging base; a flexible gas barriersurrounding surfaces of said hydraulic cylinder which are subject tocorrosion by gases present in said underground mine; and a non-corrosivegas supply for supplying a non-corrosive gas to a space between said gasbarrier and said hydraulic cylinder.
 13. A roof support for anunderground mine in accordance with claim 12, wherein said non-corrosivegas is nitrogen.
 14. A roof support for an underground mine inaccordance with claim 12, further comprising a pressure release orexhaust orifice for creating and regulating a positive pressure withinsaid gas barrier with respect to ambient pressure when non-corrosive gasis supplied to said space.
 15. A roof support for an underground mine inaccordance with claim 12, wherein said gasses present in saidunderground mine which cause corrosion include hydrogen sulfide.
 16. Aroof support for an underground mine in accordance with claim 12,wherein surfaces of said hydraulic cylinder are plated with bronze. 17.A roof support for an underground mine in accordance with claim 12,wherein said non-corrosive gas is supplied from a nitrogen gas supplyused to reduce the hazard of spontaneous combustion of coal in the mine.18. A roof support for an underground mine in accordance with claim 12,wherein there are at least two hydraulic cylinders positioned betweensaid roof engaging support and said ground engaging base.
 19. A roofsupport for an underground mine in accordance with claim 12, whereinsurfaces of said hydraulic cylinder which are subject to corrosion bygases present in said underground mine are outer surfaces of lowercylinders and upper cylinders of a two cylinder hydraulic cylinder. 20.A roof support for an underground mine in accordance with claim 12,wherein said gas barrier or enclosure comprises a flexible gas barrierwhich is attached to a lower cylinder and an upper cylinder of said atleast one hydraulic cylinder.
 21. A roof support for an underground minein accordance with claim 14, wherein said pressure release or exhaustorifice is attached to a flange which is attached to said cylinder andsaid gas barrier.